docs: def upd_scroll(self, *args):
          """Update my own ``scroll`` property to where my deck is actually
          scrolled.
  
          """
          att = 'deck_{}_hint_offsets'.format(
              'x' if self.orientation == 'horizontal' else 'y'
          )
          self._scroll = getattr(self.deckbuilder, att)[self.deckidx]